IEEE 802.15.4e is an enhanced media access control (MAC) layer protocol of IEEE 802.15.4 designed for low power and low data rate networks. The IEEE 802.15.4e architecture is defined in terms of a number of blocks in order to simplify the standard. These blocks are called layers. Each layer is responsible for one part of the standard and offers services to the higher layers. The interfaces between the layers serve to define the logical links that are described in the standard. A low-rate (LR)-Wireless personal area network (WPAN) device comprises at least one PHY (physical layer), which contains the radio frequency (RF) transceiver along with its low-level control mechanism, and a medium access control (MAC) sublayer that provides access to the physical channel for all types of transfers.
IEEE 802.15.4e is suitable for sensor devices with resource constraints; e.g., low power consumption, low computation capabilities, and low memory. As sensors and actuators that are interconnect by a personal area network (PAN) in home and office environments become more common, limiting power dissipation of each device is important. Some devices may operate on a battery, in which case frequent battery changes are undesirable. Some devices may operate on a limited amount of power that is generated by the device itself such as using conversion from solar or other light sources, scavenging from motion or thermal effects, or collection of energy from ambient electromagnetic fields.
Channel hopping is known for improving network capacity. Channel hopping can be achieved by a variety of different methods. The two most common known hopping methods are a synchronous method called Time Slotted Channel Hopping (TSCH) and an asynchronous channel hopping method defined in IEEE 802.15.4e. Many standards also exist that use such a channel hopping MAC to define MAC protocols for different applications. For example the Wi-SUN™ Alliance has published a Field Area Network (FAN) specification that specifies how to use asynchronous channel hopping for smart grid applications.
In TSCH, the time is divided into time slots, and every network device is time-synchronized to a root node in the network and uses the time slots to communicate/synchronize in the network. The device hops among all channels according to a frequency hopping sequence (FHS) during the time slots. TSCH can achieve higher capacity and provide finer granularity for power savings in IEEE 802.15.4e networks.
In asynchronous channel hopping networks, nodes hop to different channels (frequency bands) in a globally unsynchronized manner. The nodes in such networks must therefore always stay awake to enable channel hopping for achieving increased network throughput by promoting simultaneous data transfer over multiple channels between different pairs of nodes, or to achieve reliability in tough channel conditions by exploiting the channel diversity.
WPANs are used to convey information over relatively short distances. Unlike wireless local area networks (WLANs), connections effected via WPANs involve little or no infrastructure. This feature allows small, power-efficient, inexpensive network solutions to be implemented for a wide range of devices. Two different device types can participate in an IEEE 802.15.4 network include a full-function device (FFD) and a reduced-function device (RFD). An FFD is a device that is capable of serving as a personal area network (PAN) coordinator. An RFD is a device that is not capable of serving as a PAN coordinator. An RFD is intended for applications that are simple, such as a light switch or a passive infrared sensor that does not have the need to send large amounts of data and to only associate with a single FFD at a time. Consequently, the RFD can be implemented using minimal resources and memory capacity.
Although IEEE 802.15.4 supports asynchronous channel hopping networks, it does not disclose or suggest a solution for sleepy node device operation in such networks. Because sleepy nodes are required to go into a low power state where they are not be able to maintain their hopping sequence, this requires the sleepy node devices in the IEEE 802.15.4 network to therefore always stay awake to support channel hopping operation.